1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus comprising an image recording section, an image read-out section and an erasing section formed integrally with each other so that stimulable phosphor sheets are circulated and reused for recording a radiation image of an object. This invention particularly relates to a radiation image recording and read-out apparatus wherein tomographic type panoramic image recording is conducted at the image recording section.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor is first exposed to a radiation passing through an object to have a radiation image stored therein, and is then scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The light emitted from the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom in a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
Further, in a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with a radiation image recording and read-out apparatus for use in the aforesaid radiation image recording and reproducing system and moves from place to place to record radiation images for mass medical examinations, it is disadvantageous to load a mobile X-ray diagnostic station with a number of stimulable phosphor sheets, and the amount of the stimulable phosphor sheets which can be loaded on the mobile X-ray diagnostic station is limited. Therefore, it is desired to load the mobile X-ray diagnostic station with stimulable phosphor sheets which can be used repeatedly, once store the radiation images of the objects in the stimulable phosphor sheets, transfer the electric image signals read out from the stimulable phosphor sheets into a recording medium having a large storage capacity, such as a magnetic tape, and circulate and reuse the stimulable phosphor sheets for further image recording and read-out operations, thereby to obtain the radiation image signals of many objects. Further, when image recording is conducted continuously by circulating and reusing the stimulable phosphor sheets, it becomes possible to increase the image recording speed in mass medical examination. This is very advantageous in practical use.
In order to reuse stimulable phosphor sheets as described above, the radiation energy remaining in the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored therein should be eliminated or erased by the method as described, for example, in Japanese Unexamined Patent Publication No. 56(1981)-12599 or U.S. Pat. No. 4,400,619. The stimulable phosphor sheet should then be used again for radiation image recording.
Accordingly, it is desired that there be combined into a single apparatus: an image recording section for exposing each circulatable and reusable sheet composed of a stimulable phosphor to a radiation passing through an object, an image read-out section for reading out the radiation image stored in the stimulable phosphor sheet, and an erasing section for erasing the radiation energy remaining on the stimulable phosphor sheet after the read-out step for the purpose of again recording another radiation image thereon. This is because such an arrangement would make it possible to easily load the apparatus on the mobile X-ray diagnostic station to conduct medical examinations at different locations. Such an apparatus could also be easily installed in a hospital or the like. This is very advantageous in practical use.
From the aforesaid viewpoint, the applicant proposed in U.S. patent application No. 600,689 , now abandoned, a built-in type radiation image recording and read-out apparatus comprising an image recording section, an image read-out section and an erasing section combined into a single unit so that stimulable phosphor sheets are circulated and reused for image recording. In the radiation image recording and read-out apparatus, it is possible to circulate the stimulable phosphor sheets and to conduct radiation image recording, read-out and erasing continuously. However, since radiation image recording is conducted by use of various image recording apparatus in accordance with the type of the object, it is not always possible to circulate and reuse the stimulable phosphor sheets in all image recording apparatus, i.e. to constitute all image recording apparatus as the built-in type.
For example, a tomographic type panoramic image recording apparatus for recording a tomographic image of a denture jaws, jaw joints, face region or the like may be taken as an example. In the tomographic type panoramic image recording apparatus, a radiation source is secured to one end of an arm, and a cassette containing an X-ray film and an intensifying screen is secured to the other end of the arm. The radiation source and the cassette are positioned with an object intervening therebetween. The arm is rotated around the object while the cassette is exposed to a radiation passing through the object and a slit positioned between the radiation source and the cassette, thereby scanning the object with the radiation. Also, the cassette is moved in synchronization with the scanning speed, and a radiation image of a tomographic plane in the object is recorded.
When a stimulable phosphor sheet is used, instead of the aforesaid cassette, as the recording medium in the tomographic type panoramic image recording apparatus and a built-in type image recording and read-out apparatus is constituted by combining the panoramic image recording apparatus with an image read-out section and an erasing section, a complicated mechanism is required to rotate the section for holding the stimulable phosphor sheet at the image recording section and the heavy image read-out section and/or the erasing section around the object. Further, much energy is consumed for rotating them.